1. Field of the Invention
The present invention relates to a valve structure of a front fork in a two-wheeled vehicle or the like.
2. Description of the Related Art
In Japanese Utility Model Publication No. 4-7386 (patent document 1), there is disclosed a valve spring 7 in which a hole 7b inserting a seat pipe 2 thereto is formed in a center portion of a thin plate-like ring body 7a, and three arm portions 7c extending in a diametrical direction are formed in an outer periphery of the ring body 7a, as shown in FIG. 8 of the present application.
As shown in a right half of FIG. 1 in the document, the valve spring 7 is formed such a shape that each of the arm portions 7c in the outer periphery is curved upward, in a state in which a free valve 6 is seated on a taper surface 4b of an oil lock collar 4 or an initial load is applied. Further, it is also formed in a curved shape even in a free state in which the load is not applied.
Further, as shown in a left half of FIG. 1 in the document, the ring body 7a (an annular portion) in an inner periphery is deflected upward such that the free valve 6 is disengaged from the taper surface 4b of the oil lock collar 4, that is, under conditions in which the load is increased. As a result, an outer diameter (shown by reference symbol A in FIG. 8 of the present application) virtually binding leading end portions of the respective arm portions 7c in a circumferential direction is enlarged, and allows the valve spring 7 to become flat.
However, if the valve spring 7 is formed in the curved shape in the free state, there is a problem that durability of the valve spring 7 is not obtained due to a residual stress during working or the like.
Further, in Japanese Unexamined Utility Model Publication No. 63-160455 (patent document 2), there is disclosed a valve spring 7 in which a hole 7a inserting a seat pipe 2 thereto is formed in a center portion by punching a disc-like elastic body, and three oil holes 7b passing a working fluid therethrough are formed, as shown in FIG. 9 of the present application. In other words, as is shown in a right half of FIG. 1 in this document, the valve spring 7 is formed in an approximately flat shape such that the free valve is seated, and in the case that a front fork is compressed from this state, the free valve 6 is moved upward as shown by a left half of FIG. 1 in this publication, and an inner peripheral portion of the valve spring 7 is deflected upward.
However, since a leading end portion in an inner peripheral side of the arm portion 7c in the valve spring 7 is coupled by an inner ring-like portion (shown by reference symbol 7d in FIG. 9 of the present application), there is a problem that the valve spring 7 is difficult to deflect. As a result, there is a problem that a damping force during compression becomes higher and absorbability of a road surface input is deteriorated.